1. Field of the Invention
The present invention relates to a spring motor assembly for use in a Venetian blind that has no outside hanging lifting cords, more particularly to a spring motor assembly that provides a driving force for driving raising or lowering movement of slats of the Venetian blind.
2. Description of the Related Art
U.S. Pat. No. 5,482,100 discloses a Venetian blind without outside hanging lifting cords. The Venetian blind has a spring motor mounted on a top rail thereof. The spring motor is coupled to a pair of lifting cords of the Venetian blind, and provides driving forces for raising or lowering a plurality of horizontal slats that are suspended from the top rail. The spring motor includes a bracket having a back wall and a pair of side walls that extend transversely from the back wall and that cooperate with the back wall to form the bracket with a generally U-shaped configuration. The bracket further has a pair of attached plates on the side walls for fastening to the top rail. Two axles are secured onto the back wall for mounting a spring storage drum, a spring output drum and a cord spool that is co-axial and co-rotatable with the output drum. The lifting cords extend through the slats, and have lower ends connected to a bottom bar and upper ends coupled to the cord spool.
A coil spring has a first end coupled to the storage drum and an opposite second end coupled to the output drum, and is transferred from one of the drums to the other of the drums when the bottom bar moves with respect to the top rail.
When the slats are raised, the weights thereof are applied to the lifting cords, and in turn, to the cord spool and the axle that supports the cord spool. Since the axles are each connected to the bracket at only one end thereof, they are susceptible to vibration due to the weights of the slats applied thereon during operation for raising or lowering the slats, thereby adversely affecting smooth raising and lowering movement of the slats. Moreover, as the axles are fastened to the back wall by screws or rivet, loosening of the axles from the back wall is likely to occur.
Therefore, the main object of the present invention is to provide a spring motor assembly of the aforementioned type and with a firmer and more stable construction to ensure smooth raising and lowering movement of Venetian blind slats.
Accordingly, the spring motor assembly of the present invention is adapted for use in a Venetian blind that includes a top rail, a plurality of horizontal slats suspended from the top rail, a horizontal bottom bar disposed below the slats, and a pair of lifting cords, each of which extends through the slats and has an upper end extending into the top rail and a lower end connected to the bottom bar. The spring motor assembly of the present invention includes a bracket, a pair of insert plates, parallel first and second axles, a storage drum, an output drum, a cord spool, and a coil spring. The bracket is adapted to be installed on the top rail, and includes parallel front and back walls, and a pair of lateral side walls interconnecting the front and back walls and cooperating with the front and back walls to confine a receiving chamber with a top opening. Each of the front and back walls has an inner wall surface that confronts the other of the front and back walls. The front and back walls further have upper edges that define the top opening. The inner wall surface of each of the front and back walls is formed with an insert groove that extends downwardly from the upper edge and that has an open upper end formed through the upper edge. Each of the lateral side walls is formed with a cord opening communicated with the receiving chamber and adapted to permit extension of a respective one of the lifting cords therethrough. Each of the insert plates is inserted into the insert groove in a respective one of the front and back walls via the open upper end, and is retained therein. The first and second axles are mounted on the insert plates and extend transversely between the insert plates. The storage drum is mounted rotatably on the first axle. The output drum is mounted rotatably on the second axle. The cord spool is mounted rotatably on the second axle so as to be co-rotatable with the output drum. The cord spool is adapted to engage the upper ends of the lifting cords and to permit winding of the lifting cords therearound. The coil spring has a first end engaging the storage drum, and a second end opposite to the first end and engaging the output drum. The coil spring is wound around at least one of the storage drum and the output drum, and is transferred from one of the storage drum and the output drum to the other of the storage drum and the output drum when the bottom bar of the Venetian blind is moved with respect to the top rail in a vertical direction.